#include <stdint.h>
#include <sys/types.h>
-// A function to read bytes from some input source. The bytes should be
-// already unstuffed (and thus without markers).
-// A return value of -1 indicates error, a return value of 0 indicates EOF.
-typedef ssize_t (raw_input_func_t)(void*, uint8_t*, size_t);
+#include "bytesource.h"
+#include "input.h"
+
+// About 99% of all Huffman codes are <= 8 bits long (see codelen.txt),
+// and it's what libjpeg uses. Thus, it seems like a reasonable size.
+#define DEHUF_TABLE_BITS 8
+#define DEHUF_TABLE_SIZE (1 << DEHUF_TABLE_BITS)
+static const int DEHUF_SLOW_PATH = -1;
struct huffman_table {
unsigned num_codes[17]; // BITS
int maxcode[16];
int mincode[16];
unsigned valptr[16];
+
+ // Lookup table for fast decoding; given eight bits,
+ // return the symbol and length in bits. For longer codes,
+ // DEHUF_SLOW_PATH is returned.
+
+ // Note that the codes we return are 8-bit, but the type of
+ // the lookup tables is int to avoid extra zero extending.
+ int lookup_table_codes[DEHUF_TABLE_SIZE];
+ int lookup_table_length[DEHUF_TABLE_SIZE];
};
enum coefficient_class {
};
typedef struct huffman_table huffman_tables_t[NUM_COEFF_CLASSES][4];
+// Read Huffman tables from a stream, and compute the derived values.
void read_huffman_tables(huffman_tables_t* dst, raw_input_func_t* input_func, void* userdata);
+unsigned read_huffman_symbol_slow_path(const struct huffman_table* table,
+ struct bit_source* source);
+
+#include <stdio.h>
+
+static inline unsigned read_huffman_symbol(const struct huffman_table* table,
+ struct bit_source* source)
+{
+ // FIXME: We can read past the end of the stream here in some edge
+ // cases. We need to define some guarantees in the layers above.
+ possibly_refill(source, DEHUF_TABLE_BITS);
+ unsigned lookup = peek_bits(source, DEHUF_TABLE_BITS);
+ int code = table->lookup_table_codes[lookup];
+ int length = table->lookup_table_length[lookup];
+
+ if (code == DEHUF_SLOW_PATH) {
+ return read_huffman_symbol_slow_path(table, source);
+ }
+
+ read_bits(source, length);
+ return code;
+}
+
#endif /* !defined(_DEHUFF_H) */